Reforming with platinum-lead catalyst

ABSTRACT

METHOD OF PRODUCING AROMATIC HYDROCARBONS WHICH COMPRISES HYDROFORMING A HYDROCARBON AT A TEMPERATURE FROM 300*C. TO 650*C. OVER A CATALYST COMPRISING PLATINUM AND LEAD AND PREPARED BY FIRST IMPREGNATING A CARRIER WITH PLATINUM AND THEREAFTER WITH LEAD.

Aug. 6, 1974 AROMATICS YIELD NAOYA KOMINAMI ETAL REFORMING WITH PLATINUM-LEAD CATALYST Filed Nov. 18, 1971 V\ .6 Pt (TABLE I) vow/o PHTABLE II) 3,827,971 REFORMING WITH PLATINUM-LEAD CATALYST Naoya Kominami, Tokyo, and Toshiyuki Iwaisako and Kusuo Ohki, Saitama, Japan, assignors to Asahi Kasei Kogyo Kabnshiki Kaisha, Kita-ku, Osaka, Japan Continuation-impart of application Ser. No. 6,948, Jan. 29, 1970. This application Nov. 18, 1971, Ser. No.

Int. Cl. Cg 35/06; B01j 11/78 US. Cl. 208-139 4 Claims ABSTRACT OF THE DISCLOSURE Method of producing aromatic hydrocarbons which comprises hydroforming a hydrocarbon at a temperature from 300 C. to 650 C. over a catalyst comprising platinum and lead and prepared by first impregnating a carrier with platinum and thereafter with lead.

RELATED APPLICATIONS This application is a continuation-in-part of our application Ser. No. 6,948, filed J an. 29, 1970. It is related to: US. Pat. 3,827,972 which describes hydroforming of a hydrocarbon charge with a Pt-Pb catalyst prepared by other impregnation procedures; U.S. Pat. 3,827,988 which is directed to the catalysts of US. Pat. 3,827,972; and US. Pat. 3,827,973 which describes hydroforming of a hydrocarbon charge with a Pt-Pb catalyst prepared by eoprecipitation; all filed concurrently herewith.

BACKGROUND OF THE INVENTION This invention relates to a method of producing aromatic hydrocarbons from petroleum sources at high yields. More particularly, it is concerned with a method of producing a distillate of high aromatic concentration in high yield by highly selectively subjecting naphthenic hydrocarbons to dehydrogenation and parafiinic hydrocarbons to dehydrocyclization.

DESCRIPTION OF THE PRIOR ART A number of investigations have been made heretofore on methods for producing aromatic hydrocarbons from petroleum sources to establish several industrial processes employing catalysts comprising platinum, chromina, molybdena and the like. In these processes, naphtha is used as the starting material, which is subjected to catalytic reaction in gas phase at a high temperature. The liquid product thus produced contains isomers of paraffinic hydrocarbons at a high concentration and is often used as gasoline for motor cars, etc. because of its high octane number. However, its content of aromatic hydrocarbons is so low that an additional extraction or dealkylation step is needed in order to obtain benzene, toluene, xylenes and the like. In addition, the yield of aromatic hydrocarbons based on the starting material employed is so low that the operation of these steps is costly.

On the other hand, demand for aromatic hydrocarbons is being increased rapidly due to rapid growth of industries related to aromatics such as plastic and synthetic fiber industries. In this respect, it has become necessary to develop a process for producing aromatics in a higher yield. Moreover, the gasoline industry needs higher and higher octane numbers.

United States Patent O However, the existing processes will be associated with more expensive products if the yield of aromatics or the octane number is improved, and they are hardly feasible from the industrial point of view. Cracked gasoline, a byproduct in the production of ethylene, which is one of the favorable sources for aromatics, is limited in the amount of production because it depends upon the production of ethylene.

SUMMARY OF THE INVENTION As a result of extensive ingestigations on the process commercially advantageous in consideration of the source and demand of aromatics as well as the process economy as mentioned above, we have discovered a process with many advantages including the improved yield of aromatics. The present invention, derived from the discover, is concerned with a method of producing aromatic hydrocarbons which comprises treating a hydrocarbon or a hydrocarbon mixture at a temperature from 300 C. to 650 C. over a catalyst comprising platinum and lead or a catalyst comprising platinum, lead and at least a member selected from lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, zinc, cadmium, mercury, germanium, bismuth, chromium, molybdenum, tungsten, uranium, rhenium, ruthenium, rhodium, palladium, osmium and iridium. The catalyst is prepared by an impregnation procedure.

According to this invention, a variety of advantages may be enjoyed as compared with prior methods as set forth below.

First, benzene, toluene, xylenes and polymethylbenzenes are produced by quite simple procedures at low cost because of high concentration and yield of aromatics in the reformate produced according to this invention. For example, a distillate of higher boiling point than toluene or xylene in the reaction product contains neither paraffin nor naphthene and then separation can be effected by distillation only, without application of solvent extraction. Such a distinction from the prior processes is ascribed to high activity and selectivity of the catalyst of this invention in terms of aromatic formation, namely dehydrogenation or dehydrocyclization reactions.

In other words, in the conventional reforming processes known heretofore, since hydrocracking, isomerization, dehydrogenation or dehydrocyclization are the main reactions involved, an attempt to obtain a liquid fraction having a high aromatic concentration leads to an increase in hydrocracking with attendant results in low liquid yield and degraded economy. If on the other hand, the liquid yield is made higher, then the paraffin concentration in the resulting liquid becomes higher.

However, when the catalyst of the present invention is employed, quite unexpectedly, hydrocracking and isomerization are suppressed remarkably while dehydrogenation of naphthene or dehydrocyclization of parafiin occurs preferentially, and, in addition, the catalyst activity is quite high.

While lead has been shown to be a poison for a platinum catalyst in hydroforming catalysts (U.S. Pat. No. 3,000,811 of Murray et 211.), it has been found that particular Pt-Pb combinations containing specified Pb contents in specified Pb/ Pt ratios are excellent hydroforming catalysts. If the amount of Pb supported on a carrier with Pt is excessive, Pb exhibits a poisoning effect. Also, if the ratio of Pb to Pt on a carrier exceeds a specified value, then the Pt catalyst is poisoned Influencing the effectiveness of the catalysts also is the method by which they are prepared. Surprisingly, then, when the amount of Pb is controlled within prescribed limits, the Pb/Pt ratio is also so controlled, and a particular method of preparation is selected, hydroforming catalysts of high activity and high selectivity can be obtained.

Thus, utilization of features of the present invention as described above serves to produce aromatics having high carbon numbers from high boiling fractions having high carbon numbers such as, for example. kerosene and gas oil, in high yields. The same thing applies to naphtha and the process of the present invention affords far higher yields in the production of trimethylbenzene, durene and the like than known processes.

Secondly, purity and yield of hydrogen are so high that hydrogen can be supplied at a low cost.

Thirdly, life of the catalyst of this invention is so long that frequency in regeneration of the catalyst is reduced under normal reaction conditions in industrial operation.

Fourthly, the catalyst of this invention is operative at lower pressures than in prior processes. As the rate of degradation in activity in the prior catalysts is much more drastic and they become inoperative during long operation, and, therefore, the process on an industrial scale has to be carried out under high pressures. On the contrary, the catalyst of this invention is stable in the course of a long operation to give a high yield of aromatics.

As the platinum component of the catalyst, there may be used, for example, the hydroxide, platinum halides, chloroplatinic acid or hydrate or ammonium salt thereof. Especially preferred are substances containing a halogen.

This is due to the fact that in a compound containing platinum and halogen, the halogen and especially chlorine present in the compound advantageously contribute to the catalytic activity like in other platinum reforming catalysts. The preferable amount of chlorine contained in the catalyst of the present invention is in the range of 0.1-2.0% by weight and particularly in the range of 0.5-1.5% by weight based on the total weight of catalyst components. As the lead component, there may be employed the halogenides, inorganic and organic salts, hydroxide, oxide and the like. The elements used as the third component may be in the form of its oxide, hydroxide, halide or other inorganic and organic salt or complex. The platinum, lead and the third components may be in the form of a salt containing each of them.

Contents of the platinum, lead and the third components are 0.01-2% by weight, 0.01-3% by weight and -3% by weight, respectively, and preferably 0.1l% by weight, 0.1-1% by weight and 0-1% by Weight, respectively based on the total weight of catalyst components, with the ratio of lead to platinum ranging from 0.1 to 1.5 and preferably 0.2-1.0.

The catalyst is prepared by immersing a carrier in an aqueous solution containing a platinum compound such as, e.g. chloroplatinic acid, to support the platinum component on the carrier, drying the resulting material and then calcining the dried product at a temperature ranging from 300 C. to 800 C., preferably 450 C. to 600 C. The calcined product is then immersed in an aqueous solution containing a lead compound such as, e.g., lead nitrate and lead chloride, to support the lead component on the carrier, drying and calcining the resulting product at a temperature ranging from 400 C. to 700 C., preferably 450 C. to 600 C.

In the sequential impregnation method of the present invention, amounts of platinum, lead and a third component contained in the solution of the platinum, lead and third component are, in general, 0.01-2 wt. percent platinum; 0.01-3 wt. percent lead and 0-3 wt. percent third component, preferably 0.1-1 wt. percent platinum; 0.1-1 wt. percent lead and 0-1 wt. percent third component, while the weight ratio of lead supported on the carrier to platinum supported thereon ranges 0.1-1.5, preferably 0.2-1.0.

The effective Pb/Pt ratio varies depending upon the process for the preparation of catalyst and upon the reaction pressure. In case of using the catalyst prepared by the process of the present invention under atmospheric pressure and reaction pressures of 5 lrg./cm. and not less than 20 kg./cm. the maximum effective Pb/ Pt ratio are 2.2, 2.0 and 1.5, respectively. This will be illustrated by the examples as set forth hereinafter. As with the conventional catalysts, the proportion of contents of the components depends, for example, upon the type of carrier, surface area, order of the addition, method of the calcination and the like.

In order to increase the activity of the catalyst, the use of a carrier such as silica alumina, alumina, alumina hydrate, silica, zeolite, kaolin, acid clay or bentonite is effective and preferable carriers are alumina, silica alumina, zeolite and the like.

The hydrocarbons which may be used in the present invention as the starting material include those mainly comprising paraffins, olefins and naphthenes having a boiling point within the range of from 40 to 350 C., which may be used alone or in admixture of two or more kinds. Preferabe hydrocarbons are those having from 6 to 12 carbon atoms.

Most advantageous materials from the industrial standpoint are naphthas having boiling range of 40-190 0., kerosene having a boiling range of 160-260 C., and gas oil having a boiling range of 220-350 C.

Feeding ratio of hydrogen to hydrocarbon in gas volume is from 0.5 to 15 and preferably from 2 to 10. Prior to the reaction, the catalyst may be pretreated with hydrogen at or near the reaction temperature to activate it.

Feeding rae of the hydrocarbon in terms of LHSV, which stands for liquid hourly space velocity, (the feeding amount of hydrocarbon per unit time, per unit volume of catalyst, in ml.) is from 0.2 to 10 hr.- and preferably from 0.5 to 5 hrr Temperatures from 300 C. to 650 C., preferably from'430 C. to 580 C., are employed for the reaction.

The reaction pressure is dependent upon the desired quality of product and economy and may be optionally chosen within the range of from 1 to 50 kg./cm. and preferably from 5 to 20 kg./cm. In order to improve the space time yield in the commercial production, the reaction is preferably carried out under an elevated pressure.

DESCRIPTION OF PREFERRED EMBODIMENTS In order to illustrate the invention examples are given below.

Example 1 In 200 cc. of an aqueous solution containing 0.0077- 0.0155 mol./liter of chloroplatinic acid were immersed cc. of 'y-alumina having a particle size of 2-3 mm. diameter as a carrier. The resulting product was evaporated to dryness, calcined at 550 C. for 3 hours, and subsequently immersed in 200 cc. of an aqueous solution containing 00072-0036 mol./liter of lead nitrate, followed by vaporizing to dryness and calcining at 550 C. for 3 hours.

The resulting catalysts have compositions of 0.3-0.6 wt. percent platinum; 0.2-1.5 wt. percent lead and A1 0 while Pb/ Pt ratio is within the range of 0.3-2.5.

After 10 cc. of the resulting catalyst were heated at 530 C. under a hydrogen stream for 2 hours, there was passed through a layer of the catalyst maintained at 500 C. a mixed gas consisting of hydrogen and naphtha having a composition as shown below in a molar ratio of 5:1 under the total reaction pressure of 5 kg./cm. at an LHSV of 1.5 hrf Reaction results after 20 hours of operation were as tabulated in the following table:

Composition of naphtha (vol. percent):

Boiling point 88-189 C.

TABLE I Concentrations in the Reaction results solution Catalyst composition Liquid Aromatics Chloropla- Lead Pb/Pt yield yield tinic acid nitrate Pt (wt. Pb. (wt. (wt. (w (wt. Run Nos. (mol/liter) (moi/liter) percent) percent) ratio) percent) percent) 1 (Comparative) 0.0077 0. 3 0 0 80. 61. 8 2 0.0077 0. 0072 0. 3 0. 3 1.0 85. 6 72. 6 3 (Comparative)- 0. 0077 0.0144 0. 3 0. 6 2. 0 84. 1 70. 6 4 (Comparative). 0. 0077 0. 018 0. 3 0. 75 2. 5 82. 4 45. 5 5 (Comparative. 0.0155 0 0.6 0 0 79.3 63. 4 0. 0155 0. 005 0. 6 0. 2 0. 3 81. 5 69. 0 7.. 0. 0155 0. 014 0.6 0. 6 1.0 85. 3 79. 1 8 (Comparative). 0. 0155 0. 03 0. 0 l. 2 2. 0 82. 1 70. 1 9 (Comparative) 0. 0155 0.036 0. 6 1. 5 2. 5 86.1 59. 1

Example 2 Catalysts were prepared according to the same procedure as in Example 1 except that the concentrations of chloroplatinic acid and lead nitrate in the aqueous solution were altered. The resulting catalysts have compositions of 0.3-0.6 wt. percent platinum; 0.3-2.1 wt. percent lead and A1 0 while Pb/Pt ratio is within the range of 1-3.5.

After cc. of the catalyst thus obtained were heated at 530 C. under a hydrogen stream for 2 hours, there was passed through a layer of the catalyst maintained at 500 C. a mixed gas consisting of hydrogen and naphtha of the composition shown below in a molar ratio of 3:1 under a reaction pressure of 20 kg./cm. at an LHSV of 4.0 hr. Reaction results obtained after operation of 20 hours were as tabulated in the following table.

Composition of naphtha (Kuwait naphtha) (vol.

percent) Parafiin 62.0 Naphthene 26.2 Aromatics 11.8

Specific gravity API 53 .5 Boling point 210-380 TABLE II Catalyst composition Reaction results Pt (wt. Pb (wt. Pb/Pt Liquid Aromatics perper- (wt. yield (wt. yield (wt. Run Nos. cent) cent) ratio) percent) percent) 1 (Comparative) 0. 3 0 0 83. 4 49. 8 2 0. 3 0. 3 1. 0 84. 5 57. 0 3 O. 3 0.45 1. 5 85.2 50.4 4 (Comparative) 0. 3 0. 6 2. 0 89. 8 49. 3 5 (Comparative) 0. 3 0. 75 2. 5 90.5 47. 2 6 (Comparative) 0. 3 1. 04 3. 45 91. 7 36. 2 7 (Comparative) 0.41 0 0 82. 2 55. 4 8 0.41 0. 41 1.0 81. 9 58. 3 9 (Comparative)- 0. 41 0. 82 2. 0 86. 8 44. 7 10 (Comparative) a. 41 1. 04 2. 6 90. 6 43. 7 11 (Comparative) 0.6 0 0 81. 2 52. 2 12 0. 6 0. 6 1. 0 84. 3 60. 3 13 0. 6 0. 9 1. 5 85. 1 55. 2 14 (Comparative)- 0. 6 1. 2 2. 0 87. 1 50. 7 15 (Comparative)- 0. 6 1. 5 2. 5 91. 8 39. 0 16 (Comparative)- 0. 6 2. 1 3. 5 93. 4 29. 8

Data shown in Tables I and H are also shown graphically in the accompanying figure.

Comparative Example 1 Twenty milliliters of a known catalyst consisting of 0.5% platinum and 99.5% 'y-alumina were heated under hydrogen at 500 C. for 1 hour. Through the catalyst layer was passed a gaseous mixture of hydrogen and nheptane at an LHSV of 0.5 hr.'- under atmospheric pressure, while maintaining the layer at 510 C. Molar yields of the products were: Benzene 8.7%, toluene 36.7%, xylenes 3.8% and the total aromatics 49.2% after a reaction time of 1 hour.

Comparative Example 2 Fifty milliliters of a known catalyst consisting of 0.5% of platinum and 99.5% 'y-alumina were heated under Composition of the naphtha source (percent by volume):

Parafiins 48 .3

Olefins 0.4 N aphthenes 3 8.6 Aromatics 12.7

What is claimed is:

1. Method of producing aromatic hydrocarbons which comprises hydroforming naphtha under reaction conditions of a pressure ranging from 5 to 20 kg./cm. an LHSV ranging from 0.2 to 10 hr. a molar ratio of hydrogen to naphtha ranging from 2 to 10 and a temperature ranging from 430 C. to 580 C. by using a catalyst consisting essentially of from 0.1 to 1 weight percent of platinum, from 0.1 to 1 Weight percent of lead, and from 0.1 to 2 weight percent of chlorine, respectively, based on the total weight of the catalyst com ponents, and a carrier, and having a Weight ratio of lead to platinum ranging from 1 to 1.5, wherein said catalyst is prepared by impregnating 'y-alumina with an aqueous solution of chloroplatinic acid to support the platinum component on the carrier, then calcining in air at a temperature ranging from 300 C. to 800 C., impregnating the calcined platinum-chlorine/ alumina catalyst with an aqueous solution of a lead compound to support the lead component on the carrier and calcining at a temperature ranging from 400 C. to 700 C.

2. Method according to Claim 1, wherein said lead compound is lead nitrate or lead chloride.

3. Method according to Claim 1, wherein said platinum is from 0.3 to 0.6 weight percent.

4. Method according to Claim 1, wherein the reaction pressure ranges from 5 to 15 kg./cm.

References Cited UNITED STATES PATENTS 3,000,811 9/1961 Murray et al. 208- 3,649,565 3/ 1972 Wilhelm 252-466 PT 3,686,340 8/1972 Patrick et a1 260--672 R 3,670,044 6/1972 Drehman et al. 260-6833 3,425,792 2/ 1969 Stephens 232 3,761,426 9/ 1973 Wilhelm 252439 DELBERT GANTZ, Primary Examiner S. L. BERGER, Assistant Examiner 

